Ordered open-cellular carbon microstructure and method of making same

ABSTRACT

An ordered open-cellular carbon microstructure and a methods for forming the ordered open-cellular carbon microstructure capable of greatly improving the carbon yield (remaining mass % after carbonization) of an open-cellular polymer material. In one embodiment, the method starts with providing an ordered open-cellular polymer template material. The polymer template material is immersed in a reservoir containing a liquid monomer solution, wherein the liquid monomer solution swells the polymer material. Then the polymer template material is removed from the reservoir containing liquid monomer solution. Excess liquid monomer solution is removed from the polymer template material. The liquid monomer solution absorbed into the polymer template material is polymerized forming a copolymer material by irradiating the template material with ultraviolet (UV) light in a nitrogen environment. The copolymer material is heated in an inert atmosphere, wherein the copolymer material is carbonized resulting in the ordered open-cellular carbon microstructure.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to and the benefit of U.S. ProvisionalApplication No. 60/946,480, filed on Jun. 27, 2007, entitled “OrderedOpen-Cellular Carbon Microstructure And Method Of Making Same.” Theentire contents of the above-referenced application are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to an ordered open-cellular carbonmicrostructure and a method of making the same. In particular, thepresent invention relates to an ordered open-cellular carbonmicrostructure created from a low-carbon yielding polymer templatematerial.

BACKGROUND OF THE INVENTION

A number of techniques exist to create open-cellular carbon foams. Thesetechniques include the pyrolization of a polymer foam (yielding what istermed a reticulated carbon foam), chemical vapor deposition of a carbonspecies on a foam substrate, and the direct carbonization of a naturalmaterial such as wood. None of these techniques, however, can create anopen-cellular carbon material with an ordered microstructure.

Another method of carbonizing cellulose-containing plants is disclosedin Nagle, et al., “Carbonized Wood And Materials Formed Therefrom,” U.S.Pat. No. 6,670,039, which is incorporated by reference herein in itsentirety. The Nagle, et al. patent discloses that carbon foam deriveddirectly from the carbonization of a polymer must utilize a high-crosslink polymer to adequately carbonize.

An example of a carbon foam made from pyrolyzable substance to obtaincarbon foam is disclosed in Reznek, et al., “Carbon Foams And Methods OfMaking The Same,” U.S. Pat. No. 6,500,401, which is incorporated byreference herein in its entirety. However, the Reznek et al. patent doesnot disclose an open-cellular carbon material with an orderedmicrostructure.

Another method of forming vitreous carbon foams from flexiblepolyurethane foams is disclosed in Vinton et al, “Method For ThePreparation Of Vitreous Carbon Foams,” U.S. Pat. No. 4,022,875, which isincorporated by reference herein by its entirety. However, the Vinton etal. patent does not disclose an open-cellular carbon material with anordered microstructure.

A method of forming a macroporous vitreous carbon is disclosed inGilberte Moutaud et al., “Process For The Manufacture of MacroporousVitreous Carbon,” U.S. Pat. No. 3,446,593, which is incorporated byreference herein by its entirety. The Gilbertc Moutaud et al. patentdoes not disclose a method to create an open-cellular carbon materialwith an ordered microstructure.

As such, there continues to be a need for an open-cellular carbonmaterial with an ordered microstructure and the method creating thesame.

SUMMARY OF THE INVENTION

An aspect of an embodiment of the present invention is directed towardsa method for forming an ordered open-cellular carbon microstructure.

Another aspect of an embodiment of the present invention is directedtowards an ordered open-cellular carbon microstructure.

In an embodiment of the present invention, a method for forming anordered open-cellular carbon microstructure is provided. The methodincludes: providing an ordered open-cellular polymer template material,the polymer template material including an interconnected pattern ofpolymer waveguides; immersing the polymer template material in areservoir containing a liquid monomer solution; swelling the polymertemplate material with the liquid monomer solution; removing the polymertemplate material from the reservoir containing the liquid monomersolution; removing excess liquid monomer solution from the polymertemplate material; polymerizing the liquid monomer solution diffusedinto the polymer template material to form an ordered open-cellularpolymer material; heating the ordered open-cellular polymer material inan inert atmosphere to carbonize the ordered open-cellular polymermaterial to result in the ordered open-cellular carbon microstructure.

In one embodiment of the method, the polymer template material is apolyurethane material.

In one embodiment of the method, the liquid monomer solution includesacrylonitrile. The liquid monomer solution may also include a freeradical initiator to polymerize the liquid monomer solution. The freeradical initiator may be utilized to polymerize the liquid monomersolution in response to ultraviolet (UV) light. The step of polymerizingthe liquid monomer solution may include irradiating the polymer templatematerial with UV light. The polymerizing of the liquid monomer solutionmay occur in a nitrogen environment.

In one embodiment of the method, the step of polymerizing the liquidmonomer solution includes polymerizing the liquid monomer solution at atemperature ranging from about 200° C. to about 400° C.

In one embodiment of the method, the step of polymerizing the liquidmonomer solution includes polymerizing the liquid monomer solution at atemperature ranging from about 200° C. to about 300° C.

In one embodiment of the method, the step of heating the orderedopen-cellular polymer material in the inert atmosphere includes heatingthe ordered open-cellular polymer material in the inert atmosphere to atemperature not less than 600° C.

In one embodiment of the method, the step of heating the orderedopen-cellular polymer material in the inert atmosphere includes heatingthe ordered open-cellular polymer material in the inert atmosphere to atemperature not less than 800° C.

In one embodiment of the method, the ordered open-cellular polymermaterial includes a separate phase of polyacrylonitrile (PAN).

In one embodiment of the method, the ordered open-cellular polymermaterial includes a copolymer with the ordered open-cellular polymertemplate material.

In another embodiment of the present invention, a method for forming anordered open-cellular carbon microstructure is provided. The methodincludes: providing an ordered open-cellular polymer template material,the polymer template material including an interconnected pattern ofpolymer waveguides, wherein the polymer template material is apolyurethane material; immersing the polymer template material in areservoir containing a liquid monomer solution; swelling the polymertemplate material with the liquid monomer solution, wherein the monomersolution includes a free radical initiator, the free radical initiatorbeing utilized to polymerize the liquid monomer solution in response toultraviolet (UV) light; removing the polymer template material fromreservoir containing the liquid monomer solution; removing excess liquidmonomer solution from the polymer template material; polymerizing theliquid monomer solution diffused into the polymer template material toform an ordered open-cellular polymer material by irradiating thetemplate material with UV light in a nitrogen environment; and heatingthe ordered open-cellular polymer material in an inert atmosphere tocarbonize the ordered open-cellular polymer material to result in theordered open-cellular carbon microstructure.

In one embodiment of the method, the step of polymerizing the liquidmonomer solution includes polymerizing the liquid monomer solution at atemperature ranging from about 200° C. to about 300° C., and the step ofheating the ordered open-cellular polymer material in the inertatmosphere includes heating the ordered open-cellular polymer materialin the inert atmosphere to a temperature not less than 800° C.

In one embodiment of the method, the liquid monomer solution includesacrylonitrile, and the ordered open-cellular polymer material includes aseparate phase of polyacrylonitrile (PAN) or a copolymer with theordered open-cellular polymer template material.

In another embodiment of the present invention, an ordered open-cellularcarbon microstructure is provided. The ordered open-cellular carbonmicrostructure includes: a plurality of first carbonized truss elementsextending along a first direction; a plurality of second carbonizedtruss elements extending along a second direction; and a plurality ofthird carbonized truss elements extending along a third direction,wherein the first, second, and third carbonized truss elementsinterpenetrate each other at a plurality of nodes to form a continuousmaterial, and wherein the ordered open-cellular carbon microstructure isself-supporting.

In one embodiment of the ordered open-cellular carbon microstructure,the first, second, and third carbonized truss elements are defined by aplurality of polymer waveguides interconnected to each other as anordered open-cellular polymer template.

In one embodiment of the ordered open-cellular carbon microstructure,the continuous material substantially lacks interior boundaries.

In one embodiment of the ordered open-cellular carbon microstructure,the first, second, and third carbonized truss elements are adapted toaxially transfer a mechanical load applied to the ordered open-cellularcarbon microstructure.

In one embodiment of the ordered open-cellular carbon microstructure,the plurality of first carbonized truss elements, the plurality ofsecond carbonized truss elements, and the plurality of third carbonizedtruss elements include a carbonized polyacrylonitrile (PAN) material.

In one embodiment of the ordered open-cellular carbon microstructure,the plurality of first carbonized truss elements, the plurality ofsecond carbonized truss elements, and the plurality of third carbonizedtruss elements include a carbonized copolymer of polyurethane.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, together with the specification, illustrateexemplary embodiments of the present invention, and, together with thedescription, serve to explain the principles of the present invention.

FIG. 1 is a graph illustrating carbon yield differences between twopolymer formation samples as a function of temperature illustrating thebenefit of including polyacrylonitrile with polyurethane.

FIGS. 2 a and 2 b are schematic views illustrating a unit cell and anordered microstructure in accordance with embodiments of the presentinvention.

FIG. 3 is a flowchart of an exemplary method for forming an orderedopen-cellular carbon microstructure in accordance with an embodiment ofthe present invention.

FIGS. 4 a and 4 b are scanning electron micrographs of an orderedopen-cellular 3D carbon microstructure in accordance with embodiments ofthe present invention.

DETAILED DESCRIPTION

In the following detailed description, only certain exemplaryembodiments of the present invention have been shown and described,simply by way of illustration. As those skilled in the art wouldrealize, the described embodiments may be modified in various differentways, all without departing from the spirit or scope of the presentinvention. Further, the dimensions of layers and other elements shown inthe accompanying drawings may be exaggerated to more clearly showdetails. As such, the drawings and description are to be regarded asillustrative in nature and not restrictive.

Embodiments of the present invention relate to ordered open-cellularcarbon microstructures and methods to produce such microstructures.Embodiments of the present invention can greatly improve the carbonyield (remaining mass % after carbonization) of an open-cellular polymermaterial.

During pyrolyzation, or carbonization of a polymer, volatile gases arereleased resulting in mass loss, most of which occurs below 1000° C.These gases release primarily hydrogen from the polymer (in addition tooxygen and nitrogen), and depending on the molecular structure, thematerial remaining after pyrolyzation or carbonization can be a stableform of carbon. A non-limiting example of a high carbon yielding polymeris polyacrylonitrile, which if properly oxidized before carbonization,can have a carbon yield greater than 50%.

Referring to FIG. 1, if the aim is to form a carbon structure from apolymer template material, a polymer is selected to provide satisfactorycarbon yield; however, the formation process of an exemplary orderedopen-cellular polymer microstructure (as described in U.S. patentapplication Ser. No. 11/580,335) may utilize specific polymerformulations that have an extremely low carbon yield (<10 mass %), whenheated to carbonization temperatures higher than 600° C. (see graph 100in FIG. 1). For this reason, embodiments of the present inventionprovide one or more processing steps to improve the carbon yield of thepolymer material, thereby enabling formation of ordered open-cellular 3Dcarbon microstructures.

One embodiment of the present invention discloses a method for formingan ordered open-cellular carbon microstructure from a lowcarbon-yielding polymer template material (or template). Non-limitingexamples of a low carbon-yielding polymer template material having anordered open-cellular microstructure are disclosed in U.S. patentapplication Ser. No. 11/580,335, filed on Oct. 13, 2006, entitled“Optically Oriented Three-Dimensional Polymer Microstructures” and U.S.patent application Ser. No. 11/801,908, filed on May 10, 2007, entitled“Three-Dimensional Ordered Open-Cellular Structures.” The entirecontents of these two-referenced applications are incorporated herein byreference.

The method according to the present embodiment can greatly improvecarbon yield. The method involves immersing the open-cellular polymertemplate material in a liquid monomer solution that will diffuse intoand swell the polymer template material. The liquid monomer diffusedinto the polymer template material can be polymerized using eitherultraviolet (UV) light or heat. The liquid monomer is selected to have ahigh carbon yield once polymerized. A non-limiting example of such highcarbon yield monomer is acrylonitrile.

The open-cellular polymer template material acts as a template to absorbthe liquid monomer while maintaining the open-cellular microstructure.The resulting polymerized open-cellular microstructure has substantiallythe same shape as the original polymer template structure; however, thestructure can now be carbonized to form an open-cellular carbonmicrostructure with a high carbon yield. The form of the carbon formedcan range from glassy carbon to graphitic carbon depending on the needof the final application.

Another embodiment of the present invention discloses an orderedopen-cellular carbon microstructure created by the method disclosed inthe above embodiment.

An exemplary ordered open-cellular carbon microstructure disclosed inthe present invention can be useful in a wide range of applications,particularly in applications where heat and/or electrical conductivityin combination with structural integrity are required. The exemplarycarbon microstructure disclosed provides a highstrength/stiffness-to-weight ratio making it useful for compositestructural applications, and the directional nature of themicrostructure provides a preferential direction for thermal andelectrical conductivity. In addition, the ordered open-cellular carbonmicrostructure can be easily tailored, providing a way to design themechanical, as well as the thermal and electrical properties forspecific applications.

In one embodiment of the present invention, with reference to FIGS. 2 aand 2 b, a three-dimensional ordered open-cellular structure 10 (seeFIG. 2 b) is a self-supporting structure that is utilized as an orderedopen-cellular polymer template material (or template). The structure 10includes first truss elements 12, second truss elements 14, and thirdtruss elements 16. The first truss elements 12 are defined by firstself-propagating polymer waveguides and extend along a first direction A(see FIG. 2 a). The second truss elements 14 are defined by secondself-propagating polymer waveguides and extend along a second directionB (see FIG. 2 a). The third truss elements 16 are defined by thirdself-propagating polymer waveguides and extend along a third direction C(see FIG. 2 a). With reference to FIGS. 2 a and 2 b, the truss elements12, 14, 16 interpenetrate each other at nodes 18 to form a continuousmaterial.

In one embodiment, the truss elements 12, 14, 16 include a photo-polymermaterial. In one embodiment, the truss elements 12, 14, 16 are polymeroptical waveguide truss elements.

In one embodiment, the continuous material is continuously formed suchthat it lacks any interior boundaries, e.g., boundaries within theinterpenetrating portions of truss elements 12, 14, 16. In anotherembodiment, each node 18 of the structure 10 is formed of the continuousmaterial.

According to one embodiment of the present invention, the structure 10is formed by using a fixed light input (collimated UV light) to cure(polymerize) polymer optical waveguides, which can self-propagate in a3D pattern. As such, the propagated polymer optical waveguides form thestructure 10.

FIG. 3 illustrates an exemplary method 300 for forming an orderedopen-cellular carbon microstructure from a low carbon-yielding polymertemplate material according to an embodiment of the present invention.In step 302 of the method 300, a low carbon-yielding polymer templatematerial is provided. In step 304, the template material is submersed ina reservoir containing a liquid monomer solution. In one embodiment, theonly requirement for these starting materials is the originalopen-cellular polymer template material must absorb the liquid monomersolution (or monomer) and this monomer, when polymerized, must have ahigher carbon yield than the original polymer template material. In oneembodiment, the open-cellular polymer template material is apolyurethane (not highly crosslinked) material, and the liquid monomeris acrylonitrile, which behaves as a solvent and swells the polyurethaneindicating absorption. The acrylonitrile should also contain a smallpercentage (e.g., <5 wt. %) of a free radical initiator to polymerizethe monomer. The initiator could generate free radicals to causepolymerization through either heat, such as2,2′-azobis(isobutyronitrile), or UV light, such as2,2-Dimethoxy-2-phenylacetophenone or benzoin methyl ether; however, inone embodiment of the present invention, a UV photo-initiator would beused. Exposing the swelled polyurethane to UV light is done in anitrogen environment to inhibit oxygen scavenging of the free radicalsduring polymerization. The time required for polymerization can varybetween seconds to minutes, as it depends on the intensity of the UVlight, the cellular structure, and the amount of liquid monomer swelledinto the polyurethane.

The open-cellular nature of the polymer structure has a high surfacearea-to-volume ratio, which provides an ideal template (or templatematerial) to reduce diffusion time of the acrylonitrile into thepolymer. After submersing the polymer template material in theacrylonitrile for enough time to ensure maximum absorption (generally >1hr.) or swell, the open-cellular polyurethane is removed from theacrylonitrile in step 306 and the excess acrylonitrile is drained instep 308. The polymer material, now swelled with acrylonitrile and theappropriate initiator, is heated or placed under UV light (depending onthe type of initiator used) to polymerize the acrylonitrile in step 310.The new open-cellular polymer may either contain a separate phase ofpolyacrylonitrile (PAN) or the acrylonitrile could form a copolymer withthe original polymer material.

In step 312, the new open-cellular polymer material containing PAN or acopolymer of acrylonitrile is heated to a temperature ranging from about200° C. to about 300° C. (or from about 200° C. to about 400° C. or from200° C. to 300° C.), in an oxidizing environment (e.g., air) and heldthere for a period ranging from about 1 to about 5 hrs (or from 1 to 5hrs). The cyclization reaction that occurs during this heat treatment iscommonly used to improve the thermal stability of the polymer and thusthe carbon yield.

In step 314, the stabilized (or oxidized) polymer is then heated tocarbonizing temperatures that is higher than about 800° C. (or higherthan about 600° C. or high than 800° C.) in an inert atmosphere. Theresulting carbon structure will depend on the maximum temperaturereached and can range from glassy carbon to graphitic.

Scanning electron micrographs of an exemplary ordered open-cellular 3Dcarbon microstructure according to an embodiment of the presentinvention are shown in FIGS. 4 a and 4 b. Here, the orderedopen-cellular 3D carbon microstructure shown in FIGS. 4 a and 4 b isformed according to the method as described above with reference to FIG.3 and is electrically conductive and needed no metallic coating forscanning electron micrographs.

Referring back to FIG. 1, a thermogravimetric analysis (TGA) wasconducted on two samples to determine their respective mass loss whenheated to 1000° C. in Argon. The temperature ramp rate was 10°C./minute. As shown in the TGA data in FIG. 1, virtually all of thepolyurethane material was lost during carbonization; however, when thepolyurethane was incorporated with polyacrylonitrile (through the methodas described above), the mass loss at 1000° C. was approximately 50%.

In view of the foregoing, embodiments of the present invention provideordered open-cellular carbon microstructures and/or methods for formingthe ordered open-cellular carbon microstructures that can greatlyimprove the carbon yield (remaining mass % after carbonization) ofopen-cellular polymer materials.

While certain exemplary embodiments have been described in detail andshown in the accompanying drawings, it is to be understood that suchembodiments are merely illustrative of and not restrictive of the broadinvention. It will thus be recognized by a person skilled in the artthat various modifications may be made to the illustrated and otherembodiments of the invention described above, without departing from thebroad inventive scope thereof. In view of the above it will beunderstood that the invention is not limited to the particularembodiments or arrangements disclosed, but is rather intended to coverany changes, adaptations or modifications which are within the scope andspirit of the invention as defined by the appended claims andequivalents thereof.

What is claimed is:
 1. A method for forming an ordered open-cellularcarbon microstructure, the method comprising: providing an orderedopen-cellular polymer template material, the polymer template materialcomprising an interconnected pattern of polymer waveguides; immersingthe polymer template material in a reservoir containing a liquid monomersolution; swelling the polymer template material with the liquid monomersolution; removing the polymer template material from the reservoircontaining the liquid monomer solution; removing excess liquid monomersolution from the polymer template material; polymerizing the liquidmonomer solution diffused into the polymer template material to form anordered open-cellular polymer material; and heating the orderedopen-cellular polymer material in an inert atmosphere to carbonize theordered open-cellular polymer material to result in the orderedopen-cellular carbon microstructure, wherein the interconnected patternof polymer waveguides comprises: a plurality of first truss elementsextending along a first direction; a plurality of second truss elementsextending along a second direction; and a plurality of third trusselements extending along a third direction, wherein the first, second,and third truss elements interpenetrate each other at a plurality ofnodes to form a continuous material.
 2. The method as set forth in claim1, wherein the polymer template material is a polyurethane material. 3.The method as set forth in claim 1, wherein the liquid monomer solutioncomprises acrylonitrile.
 4. The method as set forth in claim 3, whereinthe liquid monomer solution comprises a free radical initiator topolymerize the liquid monomer solution.
 5. The method as set forth inclaim 4, wherein the free radical initiator is utilized to polymerizethe liquid monomer solution in response to ultraviolet (UV) light. 6.The method as set forth in claim 5, wherein the polymerizing the liquidmonomer solution comprises irradiating the polymer template materialwith UV light.
 7. The method as set forth in claim 6, wherein thepolymerizing the liquid monomer solution occurs in a nitrogenenvironment.
 8. The method as set forth in claim 1, wherein thepolymerizing the liquid monomer solution comprises polymerizing theliquid monomer solution at a temperature ranging from about 200° C. toabout 400° C.
 9. The method as set forth in claim 1, wherein thepolymerizing the liquid monomer solution comprises polymerizing theliquid monomer solution at a temperature ranging from about 200° C. toabout 300° C.
 10. The method as set forth in claim 1, wherein theheating the ordered open-cellular polymer material in the inertatmosphere comprises heating the ordered open-cellular polymer materialin the inert atmosphere to a temperature not less than 600° C.
 11. Themethod as set forth in claim 1, wherein the heating the orderedopen-cellular polymer material in the inert atmosphere comprises heatingthe ordered open-cellular polymer material in the inert atmosphere to atemperature not less than 800° C.
 12. The method as set forth in claim1, wherein the ordered open-cellular polymer material comprises aseparate phase of polyacrylonitrile (PAN).
 13. The method as set forthin claim 1, wherein the ordered open-cellular polymer material comprisesa copolymer with the ordered open-cellular polymer template material.14. A method for forming an ordered open-cellular carbon microstructure,the method comprising: providing an ordered open-cellular polymertemplate material, the polymer template material comprising aninterconnected pattern of polymer waveguides, wherein the polymertemplate material is a polyurethane material; immersing the polymertemplate material in a reservoir containing a liquid monomer solution;swelling the polymer template material with the liquid monomer solution,wherein the monomer solution comprises a free radical initiator, thefree radical initiator being utilized to polymerize the liquid monomersolution in response to ultraviolet (UV) light; removing the polymertemplate material from the reservoir containing the liquid monomersolution; removing excess liquid monomer solution from the polymertemplate material; polymerizing the liquid monomer solution diffusedinto the polymer template material to form an ordered open-cellularpolymer material by irradiating the template material with UV light in anitrogen environment; and heating the ordered open-cellular polymermaterial in an inert atmosphere to carbonize the ordered open-cellularpolymer material to result in the ordered open-cellular carbonmicrostructure.
 15. The method as set forth in claim 14, wherein thepolymerizing the liquid monomer solution comprises polymerizing theliquid monomer solution at a temperature ranging from about 200° C. toabout 300° C., and wherein the heating the ordered open-cellular polymermaterial in the inert atmosphere comprises heating the orderedopen-cellular polymer material in the inert atmosphere to a temperaturenot less than 800° C.
 16. The method as set forth in claim 14, whereinthe liquid monomer solution comprises acrylonitrile, and wherein theordered open-cellular polymer material comprises a separate phase ofpolyacrylonitrile (PAN) or a copolymer with the ordered open-cellularpolymer template material.